Telephone system



p 1931. w. H. PAULETT ET AL 1,323,665

TELEPHONE SYSTEM Filed Sept. 3. 1929 '7 Sheets-Sheet l OPERATE 0N l/ZJ/R07. STEP 1mm William H BEE FaulETT 1111' I5 Eill'n s Sept. 15, 1931.

W. H. PAULETT ET AL TELEPHONE SYSTEM Filed Sept. 3. 1929 '7 Sheets-Sheet2 3 EE 0 in 1 I N Es "E 6 Q.

1 Inuaniurs William H223 Paul??? ar'le s Eillin s Sept. 15, I931. w. H.PAULETT ET AL 1,823,665

TELEPHONE SYSTEM Filed Sept. 3. 1929 7 Sheets-Sheet 5 William HearPaul's 2'2" ZLEI'ZES' Billings p 15, 1931- w. H. PAULETT ET AL 1,823,665

TELEPHONE SYSTEM Filed Sept. 3. 1929 7 Sheets-Sheet 5 -Iniraniurs 'w-zz-H F 1 I 5% z sifiiig Sept. 15, 1931. w. H. PAULETT ET AL 1,823,665

TELEPHONE SYSTEM Filed Sept. 3. 1929 7 Sheets-Sheet 6 1mm WilliamHsw'paulifi a ii-flar'lss 13min 5 P 5, 1931- w. H. PAULETT ET AL1,823,665

TELEPHONE SYSTEM Filed Sept. 5. 1929 7 Sheets-Sheet 7 I'm??? WilliamHsnr Paul??? Charles Gillin s Patented Sept. 15, 11931 WILLIAM HENRYLPA'ULETT' AND CHARLES GILLINGS, OF LIVERPOOL, ENGLAND, A'SSIGNORS TOASSOCIATED TELEPHONE AND TELEGRAPH COMPANY, OF CHICAGO, ILLINOIS, ACORPORATION OF DELAWARE TELEPHONE SYSTEM Application filed September 3,192.9,Seria1 No. 390,}55, and in Great Britain September 5, 1928.

The present invention relates to telephone systems and is moreparticularly concerned with arrangements for holding switches operatedin such systems and for providing arrangements for testing whether aline is free or busy. A well-known type of telephone system employsstep-by-step switches which are guarded by the application of earthpotential to the test contacts, the absence of earth potential from thetest contacts being employed to indicate that the switch s in acondition to be taken into use for setting up aconnection.

One object of the p esent invention is to mark the idle condition of theswitches in a more positive manner without complicating the circuitdetails or the construction of the switches and this is effectedaccording to one feature of the invention by connecting one 'pole ofbattery to the associated test contact when a line is free andconnecting the other pole of battery to the associated test contact whena line is busy.

In the system above referred to, unless special arrangements are -madethere is a possibility that a switchmay be taken into use after it hasbeen released by a calling party but before it has restored to normal.Such arrangements are readily provided according to another feature ofthe invention by which the switches are adapted to be maintained inoperated position by the application of potential to a holding conductorwhilst they are marked busy due to the presence of the holding potentialand also due to the absence of special idle potential so that aswitch-may be released by the removal of the holding potential withoutrendering it available for useuntil idle potential is restored.

According to a further feature of the invention a holding conductorwhich is adapted to maintain. a plurality of switches operated extendsover the test wipers of the switches, potential different from that usedfor holding being employed to designate an idle line.

The invention will be better understood from the following descriptionof several 50 methods of carrying it into efi'ect which should be takenin conjunction with the ac companying drawings. It will be understoodthatthe particular arrangements shown and described are given by way ofexample only and that the invention is not limited to these precisearrangements.

Referring now to the drawings, these show in the usual manner circuitsof automatic switches according to the invention for use in variouscircumstances. All the switches are assumed to be of the well-knownvertical and rotary type having their contacts arranged in rows.

Fig. 1. represents an intermediate group selector, that is to say one inwhich all br1dges across the line are cut out and a straight-throughconnection obtained when the switch has been completely set. This switchmay be taken into use either from a lineswitch or from a selector whichmay be of simllar type or may be. of the battery feeding type.

Fig. 2 indicates a similar switch provided however withtwo sets ofwipers and corresponding bank contacts and arranged for simultaneoushunting over both banks so that testing of two lines takes place at thesame time.

Fig. 3 is a first selector with transmissio bridges for supplying feedcurrent to the calling party and giving operator hold facilities. Thisswitch is accessible from a subscribers lineswitch.

Fig. 4 is an incoming selector accessible over a two-conductor trunkline.

Fig. 5 is a final selector or connector which connects directly with awanted partys line and supplies ringing current and subsequently batteryfeed to the wanted line.

Fig. 6 shows a first selector substantially similar to Fig. 3 exceptthat it is arranged for metering at the end of the conversation ratherthan upon the reply of the called party.

Fig. 7 is a first selector similarly arranged for metering at the end ofa conversation, but in this case by a booster impulse over the test leadinstead of by connection of potential to a separate metering lead.

The operationof the various switches will now be considered in detail.Referring first to Fi 1, when the switch is seized by the compfiation ofa loop across conductors 1. and 2, a circuit is completed for line relayA which thereupon operates and at armature 10 completes a circuit forthe upper winding of relay B. Relay B at armature 11 removes the normalbattery connection to test lead 3 which is supplied over oil-normalsprings 24 and armature 8 and its back contact. This battery potential,which 'is applied through a comparatively high resistance, is necessaryto mark the switch idle and permit it to be taken into use from apreceding selector. In case the switch is seized from a subsqriberslineswitch which is arranged to hunt for absence of earth as is moreusually the practice it will be-necessary for earth to be applied toconductor 3 by the operation of armature 11 as is shown in the drawings,and in this case the battery connection is superfluous. The switch mayhowever be wired as shown in which case it will operate in either set ofcircumstances without change. Relay B moreover at armatures 12, 13 and14 prepares circuits for relay H, relay G and rotary mag- 7 net Brespectively, and at armature 15 opens a point in the release magnetcircuit and prepares the impulsing circuit for the vertical magnet V.

When the next series of impulses is transmitted, relay A willde-energize intermittently and on each deenergization will com- 7 pletea circuit from earth, armature 7 and its back contact, armature 10 andits back contact, winding of relay 0, armature 15 and its front contact,cam springs 21, winding of vertical magnet V to battery. The verticalmagnet is accordingly energized intermittently and operates to raise thewipers 2729 a corresponding number of steps. Relay C which is slow torelease remains energized throughout the impulse series and at armature16 opens a point in the rotary magnet circuit.

l At the end of the series of impulses relayC de-energizesand a circuitis then completed for the rotary magnet from earth, armature 7 and itsback contact, oif-normal springs 26, back contact and armature 16, backcontact and armature 17, armature 14 and its front contact, winding ofmagnet R to battery.

Wipers 2729 are accordingly advanced one step to engage the first set ofcontacts in the level chosen and the magnet also operates the springs 19therebcy;Ir completing a circuit for relay G. Relay at armature 18prepares a testing circuit for relay H and at armature 17 opens thecircuit of the rotary magnet so that this magnet de-energizes and opensthe circuit of relay G. In case the line which the wipers are nowengaging is free, wiper 27 will encounter battery and a circuit willthen be completed to cause the operation of relay H. If the line is inuse, however, there will be earth on the associated test contact or incase the test lead should be broken the contact will be dead and ineither case it will be impossible for relay H to operate. Accordingly assoon as relay G de-energizes, a circu1t is again completed for therotary magnet and the same cycle of operations takes place, the wipersbeing advanced a further step. This continues until a free line isencountered, whereupon relay H energizes over its lower winding and atits lightly-tensioned subsequently. Relay B is sufficiently slow toensure that earth shall be maintained on the test conductor until it isfed back from the switch just taken into use. It may be pointed out thatthe provision-of a make spring connected to earth for off-normal spring24 is only necessary in the case in which the switch is accessible froma rotary lineswitch which is arranged to hunt for absence of earth inthe usual manner. In case the switch were accessible from a selector ofsimilar type the front contact of armature 11 could be omitted and alsothe make contact of ofi-normal spring 24 and in this event it would alsobe possible to dispense with armature 8 which is only inserted toprevent relay H being permanently locked up to'the earth on the operatedofl-normal spring 24.

In case the switch should be unable to find a free line it would beadvanced to the eleventh rotary position and cam springs 20--23 wouldthen be Operated. Thereupon at springs 20 busy tone and flash batteryare connected up over lead 31 to the'lower winding of relay A, at spring21 a circuit is completed from the busy hold lead 30 for the lowerwinding of relay B to maintain this relay energized while relay A isde-energized during the battery period, at spring 22 a circuit iscompleted for maintaining relay G energized so as to prevent any furtheroperation of the rotary magnet and at spring 23 earth is applied to testwiper 27 to operate an overflow meter which may be common to a number ofswitches.

The release of the switch is brought about by the removal of earth fromthe test conductor whereupon relay H is de-energized and at armature 7completes a circuit for the release magnet Z in series with relay Cwhich accordingly operates though without useful effect at this time. Itwill be noted that the switch is not rendered available for re-seizureuntil it has reached its normal position whereupon and the circuit ofthe release magnet is opened at springs 2'".

Referring now to Fig. 2. the circuits of the switch there shown aresimilar except that the switch is provided with two sets of wipersarranged for simultaneous hunting. Moreover the guarding circuit isslightly different in that the battery potential indicating the idlecondition is applied over a back contact of relay C andaccordingly theswitch is not available for use until a short interval after theoperation of the release magnet.

The various circuit changes which take place during the operation of theswitch will be traced through briefly. \Vhen the switch is seized by thecompletion of a loop across conductors 51 and 52, relay- A operates andat armature 6G completes a circuit for relay B which thereupon atarmature 67 removes idle potential and applies guarding potential to thetest conductor 53, at armature (S8 prepares a circuit for relay G atarmature (59 prepares circuits for relays HA and HB and at armatures 70and 71 prepares circuits for the rotary magnet R and vertical magnet Vrespectively. Vfhen the next series of impulses is transmitted, relay Ade-encrgizes intermittently and sends a corresponding number of pulsesto the verti*al magnet which operates to raise the wipers 83-88 to thedesired level. Relay C is energized in series with the verti .al magnetthroughout the train of impulses and at armature 73 maintains thecircuit of the rotary magnet open. \Vhen relay C de-energizes, however,magnet R is energized to rotate the wipers one step into engagement withthe first set of bank contacts and at springs 76 to complete a circuitfor relay G. This relay at armature 74 opens the circuit of the rotarymagnet thus causing it to open contacts 76 and at armature 75 completesthe test circuit for relays HA and HB. If test wipers 85 and 88 bothfail to encounter battery due to the associated lines being busy or outof order, neither of these relays can operate and on the de-energizationof relay G the rotary magnet is again energized to advance the wipersanother step. If wiper 88 now encounters battery while wiper 85encounters earth relay HB will be shortcircuited but a circuit will becompleted from battery on wiper 88 over bank contact and armature 61,lower winding of relay HA, front contact and armature 69, front contactand armature 75 to earth. Relay HA upon operating in this circuit, atarmatures 54 and 59 switches leads 51 and 52 through to wipers 86 and87, at armature 55 feeds earth forward to wiper 88 to busy the seizedline,at armature 56 disconnects wipers 85, at armature 57 completes alocking circuit for itself over its upper winding and at armature 58opens a point in the circuits of the release and rotary magnets. In casewiper 85 had encountered battery while wiper 88 had encountered earth,

relay HB would have operated and at armature 6065 would have producedsimilar changes to those produced by relay HA. In case wipers 85 and 88both encountered battery both relays HA and HB would have commenced tooperate but owing to the fact that relay HE is provided'with a copperslug which makes it slightly slow to energize relay HA energizes firstand at armature 56 opens the circuit of relay HB. By this means adefinite choice is given when two idle lines are encounteredsimultaneously, and this arrangement is very desirable in case gradingis employed between the various groups of switches. If the switch hadbeen unable to find a free line in either bank, it would have beenadvanced to the eleventh position and the am springs 7 780 would thenhave been operated. Thereupon at springs 77 busy tone and flash batteryare connected up over lead 90 to the lower winding of relay A, atsprings 78 a circuit is completed for the lower winding of relay B fromthe busy hold lead 89 to maintain this relay during the flash batteryperiod, at springs 79 a locking circuit is completed for relay G toprevent any further operation of the rotary magnet and at springs 80earth is fed forward to test wiper 88 to operate a suitable overflowmeter. The release of the switch takes place when earth is removed fromthe test conductor whereupon relay HA or HB as the case may be'willdeenergize and complete a circuit extending from earth, back contact andarmature 64, armature 58 and its back contact, armature 66 and its backcontact, winding of relay C, armature 71 and its back contact,olf-normal springs 81, winding of release magnet Z to battery. Magnet Zand relay C operate in series in this circuit, the former restoring theswitch shaft and wipers in the usual manner and the latter at armature72 applying earth to the test conductor 53 in place of battery so as toprevent seizure of the switch at that time. When the switch hascompletelyrestored, oft-normal springs 81 will open and relay C willcommence to release so that after a short interval battery will bereplaced on test conductor 53 and the switch will be available forfurther seizure.

Referring now to Fig. 3, this shows a battery feeding first selectorwhich is assumed to be accessible from a rotary lineswitch of the typewhich hunts for absence of earth so that it is unnecessary to provide abattery connection to the test conductor to indicate that the switch isin condition to be seized. This switch is also provided witharrangements for metering over a fourth wire when the called partyreplies. When the switch is taken into use, relay A is energized overleads 101 and 102 and the calling loop and at armature 105 prepares acircuit for repeating impulses to succeeding switches and at armature106 completes a circuit for relay AB. The latter relay upon operating,at armature 107 opens a point in the operator hold circuit which will bemore fully described subsequently and at armature 108 completes acircuit for relay B. Relay B thereupon at armature 109 completes acircuit over armature 117 and its bank contact for the supervisory lampCSH and over off-normal spring 133 for relay MD- and prepares a numberof other circuits, at armature 110 applies earth to the test conductor103 to maintain the lineswitch operated, at armature 111 prepares acircuit for relay H and at armature 112 opens a point in the circuit ofthe release magnet Z and prepares a circuit for the vertical magnet V.Relay MD completes a locking circuit for itself at armature 126, atarmature 127 opens a point in the metering circuit and at armature 128closes a point in the operator hold circuit for relay 1. Moreover atthis time dial tone from lead 140 is connected up over off-normalsprings 132 to conductor 101 to indicate to the callin party that he maynow operate his dia switch. a

When the first series of impulses is transmitted, relay A de-energizesintermittently, thereupon at armature 106 transmitting acorresponding'number of pulses to the vertical magnet V whichaccordingly operates to raise the wipers 137139 a corresponding numberof steps. Relay 0 which is slow to release is energized in series withthe vertical magnet throughout the impulse series and at armature 115opens a point in the circuit of the rotary magnet, another point beingclosed at springs 135 as soon as the switch goes offnormal. At the endof the vertical movement relay C de-energizes and a circuit is thencompleted from earth, armature 109 and its front contact, back contactand armature 119, armature 115 and its back contact, off-normal springs135, armature 125 and its back contact, winding of rotary magnet B tobattery. Magnet B accordingly advances the wipers 137-139 intoengagement with the first set of bank contacts and at springs 136completes a circuit for relay G which thereupon at armature 119 opensthe circuit of the rotary magnet and at armature 118 completes a testingcircuit for the upper winding of relay H to test wiper 139. If the linenow connected with is busy or out of order as indicated by the absenceof battery on the test contact, relay H will be unable to energize andwhen relay de-energizes due to the release of rotary magnet R, thecircuit of this magnet will be again completed and it will operate to advance the wipers a further step. When a free line is encountered,battery picked up by wiper 139 will be extended over armature 111 andits front contact, upper winding of relay H, front contact and armature118 to earth. Relay H-upon operating at this time, at arma tures 120 and125 connects the speaking leads through to wipers 137 and 138, atarmature 121 closes a point in the metering circuit, at armature 122feeds earth forward to wiper 139 to busy the seized line, at armature123 completes a locking circuit for itself over its lower winding, atarmature 124 disconnects the vertical magnet and substitutes aconnection to battery through a resistance and at armature 125 opens apoint in the circuit of the rotary magnet to prevent any furtheroperation of this magnet. A loop is now completed across wipers 137 and138 which extends as follows: wiper 137, armature 120 and its frontcontact, armature 105 and its front contact, left-hand winding ofpolarized relay D, winding of relay 1, front contact and armature 125,wiper 138 and this loop serves to prepare the succeeding switch foroperation in the usual manner.

When the next series of impulses is transmitted, relay A pulses asbefore and at armature 105 intermittently opens the loop circuit justtraced so as to produce operation.

'of the succeeding switch in the usual manner. Moreover at armature 106a circuit is completed intermittently for relay 0 which thereforeenergizes and at armature 114 short-circuits relays I and D so as togive a better impulsing circuit. Succeeding trains of impulses aretransmitted in the same way to set the various switches and if thecalled partys line is idle at this time it is connected with and hisbell is rung. When he replies by removing his receiver, current flowover the speaking conductors is reversed at the final selectorswitch andthis serves to effect the operation of polarized relay D whichaccordingly at armature-117 extinguishes lamp CSH and opens the lockingcircuit of relay MD and also closes another point in the meteringcircuit. Relay MD is slow to release and de-energizes after a shortinterval thereupon at armature 127 extendin earth on armature 109 to themetering lea 104 to effect the operation of the calling partys meter.

The subscribers may now converse as desired and when they have finishedthey will replace their receivers. If the called party replaces hisreceiver first, relay D will deenergize and again complete a circuit forthe lamp CSH which accordingly serves to indicate when the called partyis being held by the calling party. When the calling party replaces hisreceiver, relay A de-energizes and at armature 105 opens the loopextending to the succeeding switches so as to cause their release in theusual manner and at armature 106 opens the circuit of relay AB andcompletes the circuit of relay C. Relay AB on de-energizing after ashort interval opens the circuit of relay B which thereupon at armature110 connects up armature 113 which is at this time in operated position.Relay B also at armature 112 completes a circuit for release magnet Z,in series with relay C and the magnet operates to release the switch.Earth is maintained on test conductor 103 until restoration is completeand the circuit of magnet Z and relay 0 is accordingly opened atoff-normal springs 134.

In case the switch'should be unable to find a free line in the selectedlevel, it would be advanced to the eleventh rotary position thuscausingv the operation of the cam springs. 'lhereupon at. springs 129busy tone over lead 111 is connected to lead 101 to inform the callingparty that he cannot obtain his connection, at springs 130 earth isconnected to test wiper 139 to operate an overflow meter and at springs131 a locking c1rcu1t 1s completed for relay G to prevent any furtheroperation of the rotary magnet. Release s eiiected when the callingparty replaces hls receiver whereupon relay A de-energizes with theresult previously described. There is no necessity in this case forconnecting up busy flash battery since the switchshown is onlyaccessible from a subscribers llneswltch and not from an operatorsposition. If connection is extended to an operators position in whichcase it is desirable'that the operator should control the release of theconnection no battery reversal will take place and consequently sincerelay D does not operate relay MD will remain operated and no meter ingwill be efi'ected. Furthermore the connections at the operators positionW111 be such that battery is applied to the lower speaking lead as wellas to the upper speaking lead. Consequently when the calling partyreplaces his receiver at the end of the conversation and relays A and ABde-energize, a. circuit is completed from earth, armature 107 and itsback contact, armature 128 and its front contact, winding of relay I tobattery on the lower speaking lead. Consequently relay I is maintainedenergized and at armature 116 provides an alternative c1rcuit for relayB so that release cannot take place until battery is removed from thelower speaking lead when the operator takes down the connection.

Referring now to Fig. 4, this shows an 1ncoming selector, that is tosay, a selector which is adapted to be seized over a two-wire junctionso that in this case it is clearly impossible for the switch to feedback battery on the test conductor in order to indicate 1ts idlecondition. The arrangement adopted is that in the bank of the switchhaving access to the outgoing and of the trunk line a permanent batteryconnection is made to the associated test contact so that if the trunkline is tree this battery connection will be effective. If, however, theline is in use earth will be connected to the test contact in the usualmanner, and this will have the eflect of rendering the batteryconnection ineli'ective. When the switch shown in Fig. 4 is seized bythe connection of a loop across the speakfor relay H, at armature 162prepares a test circuit for this relay, at armature 163 prepares anumber of circuits and lights the supervisory lamp CSH, and at armature164 prepares the impulsing circuit, When the next series of impulses istransmitted, relay A de-energizes intermittently and on eachde-energization completes a circuit at armature 157 extending overarmature 181 and its back contract, winding of relay C, arma-.

ture 164 and its front contact, armature 176 and its back contact,winding of vertical magnet V to battery, so that magnet V operates tostep wipers 183-185 to the required level. Relay C being slow to releaseremains energized throughout the train of impulses and at armature 165opens a point in the rotary magnet circuit, at armature 166short-circuits relays I and D and at armature 167 completes a circuitfor the upper winding of relay I which accordingly operates but withouteffect at this time. When relay C de-energizes at the end of the trainof impulses, the circuit of the rotary magnet is completed from earth,armature 163 and its front contact, armature 175 and its back contact,armature 170 and its back contact, back contact and armature 165,oil-normal springs 187, winding of magnet R to battery. The rotarymagnet operates to step the wipers into engagement with the first set ofbank contacts and closes its springs 185 thereby completing a circuitfor relay G which at armature 17 0 opens the circuit of magnet R and atarmature 170 opens the circuit of magnet R and at armature 171 completesa testing circuit for the upper winding of relay H. Relay H is not 0erated unless the test wiper 185 picks up attery indicating that theline is idle and if this does not occur, when relay G again de-energizesowing to the opening of its circuit at springs 185 it again completes acircuit for the rotary magnet B so that the wipers are advanced afurther step. When an idle line-is reached, relay H is operated frombattery picked up by the test wiper and at armatures 172 and 177switches the speaking leads through to wipers 183 and 184, at armature173 connects earth to test wiper 185, at armature 17 4: locks itself upover its lower winding, at armature 175 opens the rotary magnet circuitand prepares a circuit for relay BP and at armature including relays Iand D is now placed across- 176 disconnects the vertical magnet. A loopoperated at armature 167 "and S11 sequent series 1 of impulses arerepeated in the same" way.' The arrangement whereby relay-"I ismaintainedsaturated also reduces the impedance when relays I and D- aresubsequently re-inserted in the 100 and this overcomes any tendency forthe line relay of the distant switch to de-energize momentarily and givea false impulse. When the connection. has been completely set up and thewanted party replies, the current flow over the speaking conductors isreversed at the final selector and is then in such a direction as tooperate relay D. This relay accordingly at armature 169 opens thecircuit of the'supervisory lamp OSI-I' and completes the circuit ofrelay DR which at armature 153 opens a further point. in the operatorshold circuit and at armatures 154: and 155 reverses the connections ofrelay A to conductors 151 and 152 thus repeating back the supervisorysignal.

At the end of the conversation when the wanted party replaces hisreceiver relay D is again de-energized and connects up the lamp CSH' theprolonged lighting of which accordingly indicates that the called partyis being held. When the calling party replaces his receiver, relay Ade-ener zes and releases relay AB at armature 15 and at armature 156opens the loop to the succeedingswitches so as to effecttheir release 1nthe usual manner. Relay AB opens the 01rcuit of relay B and when relay Bhas deenergized the circuit of the release magnet is completed asfollows: earth, armature 157 and its back contact, armature 181 and itsback contact, winding of relay C, armature 164 and its back contact,off-normal springs 186, winding of magnet Z'to battery. The releasemagnet operates to restore the switch to normal and relay C is alsoenergized though without any particular effect in this case.

If the switch had been unable to find a free line in the selected levelit would have been advanced to the eleventh position,-thereuponoperating the cam springs. At springs 188 earth is connected to testwiper 185 to operate an overflow mzeter connected to the eleventhcontact, at springs 189 a locking circuit is com leted for relay G so asto prevent any urther operation of the .rotary magnet andat springs 190interrupted earth is again over lead 191 is connected to relay BF whichaccordingl energizes and de-energizes intermittent y. Thereupon atarmature. 182 batte is connected up to the lower winding 0 relay A inplace of the normal earth connection, at armature 181 the impulsingcircountered beyond the switch shown in Fig.

4, battery and earth intermittently-will be applied to the lowerspeaking conductor.

uring the application of battery, relay I is de-energiz'ed and a circuitis then completed as follows: battery, lower winding of relay BP, backcontact and armature 178, front contact and armature159, back contactand armature 168, front contact and armature 175, front contact andarmature 163 to earth. Relay BP is a two-step relay and at this timeoperates only its light armature 179 thereby preparing a locking circuitfor itself. On

the termination of the battery period, relay I again energizes therebyat armature 168 removing the short-circuit fromthe upper winding ofrelay BP which thereupon energizes fully and at armature. 178 prepares acircuit for .relay BF. When relay I next de-energizes the circuitpreviously traced will be extended to relay BF which will accordinglyenerg'me with the results previously described. Relay I will nowcontinue to operate in synchronism with the busy flash pulses and relayBF will pulse similarly thereby repeating the busy signal back to thecalling party.

In case the connection is extended to. an operators position, it isdesirable that the operator should have control of the release as wasdescribed in connection with Fig. 3. In this case no reversal will takeplace and consequently relays D and DR will not be operated but as longas the connection remains set up battery will be connected to the lowerspeaking conductor. When the calling party rep-laces his receiver,relays A and AB will be de-energized and a circuit will then becompleted from earth, armature 158 and its back contact, armature 153and its back contact, lower winding of relay I to battery connected tothe lower speaking conductor so that relay I will remain operated and atarmature 168 will complete an alternative circuit for relay B so thatthe connection remains held up. Moreover owing to the fact that relay Bis now energized while relay AB is (lo-energized, the battery connectionto the lower speaking conductor is repeated back over front contact andarmature 164 and normally closed springs controlled by armature 160 tolead 152 to hold up the preceding switches.

Referring now to Fig. 5, this represents a final selector or connectorswitch, that is to say one which is adapted to connect with a wantedline and does not perform any hunting operation. This switch is assumedto be accessible over selectors modified according to the invention, forinstance, as shown in any of Figs. 1-4. When the switch is taken intouse by the completion of a 100 across conductors 201 and 202, linerelayis operated and at armature 207 completes a circuit for the lowerwinding of relay B. Relay B upon operating, at armature 208 removes thenormal battery connection from test lead 203 and replaces it by earth,at armature 209 prepares circuits for relays E, F and H and at armature210 disconnects the release magnet Z and prepares the circuit of thevertical magnet V. When the next series of impulses is transmitted,relay A de-energizes intermit-' tently in accordance therewith and oneach de-energization completes a circuit from earth, armature 207 andits back contact, armature 210 and its front contact, armature 219 andits back contact, armature 231 and its back contact, lower winding ofrelay 0 to battery and in parallel therewith armature 223 and its backcontact. winding of vertical magnet V to battery. The vertical magnet isoperated in the usual manner to raise wipers 233235 to the requiredlevel. and relay C is also operated and since at armature 212 itshort-circuits its upper winding it is rendered slow to release and thusremains energized throughout the train of impulses. At

armature 211 it prepares a circuit for relay G which is not-yetoperative. at armature 213 it opens a point in the busy flash circuitand at armature 214 shunts armature 219 and 231 though this also iswithout eifect at this stage. On the termination of this series ofimpulses, relay C de-energizes and a circuit is then completed asfollows: earth, armature 209 and its front contact, armature- 228 andits back contact, back contact and armature 212, off-normal springs 237,windingof relay E to battery. Relay E upon energizing at this time, atarmature 222 completes a locking circuit for itself independent of relayC and at armature 223 connects up the rotary magnet R in place of thevertical ma gnet V. When the final series of impulses is transmitted,relay G is energized over the same circuit as before and impulses aretransmitted to the rotary magnet R which accordingly steps the wipersinto engagement with the contacts associated with the wanted line. Theupper winding of relay G is new connected to test wiper 235 so that ifbusy contacts are passed over during the rotary movement relay G will beenergized. This however produces no detrimental effect since the busycircuit is held open at armature 213 and the impulsing circuit ismaintained intact at armature 214.

Suppose in the first instance that the wanted line is busy when it isconnected with; in this case wiper 235 will encounter earth andtherefore relay G will be operated when the wipers come to rest.Accordingly when relay C de-energizes, a locking circuit is completedfor the upper winding of relay G over the normally closed springscontrolled by armature 211 and at armature 218 busy flash battery isconnected to the lower winding of relay A, while at armature 219 acircuit is completed for the upper Winding of relay B to the busy holdlead 239 when relay A deenergizes during the battery periods.Accordingly the usual busy signal is repeated back to the calling partywho will realize that he cannot obtain his connection and thereforereplaces his receiver. When this is done relay A de-energizes andaccordingly during the next earth period of the busy flash, relay Bde-energizes also. On the de-energlzation of relay B the release magnetcircuit is completed from earth, armature 207 and its back contact,armature 210 and its back contact, off-normal springs 236, releasemagnet Z to battery and in parallel thereto, lower winding of relay G tobattery. Relay G is accordingly maintained energized until the switchhas reached normal position and at armature 216 removes the batteryconnection indicating the idle condition so as to ensure that the switchshall not be again taken into use until it has fully restored.

Assume now that the wanted partys line is idle when it is connectedwith; in this case when the rotary movement terminates wiper 235 willnot encounter earth and relay G will be de-energi zed. A circuit is thencompleted from earth, armature 209 and its front contact, armature 217and its back contact, lower winding of relay H, back contact andarmature 211, test wiper 235, cut-01f relay and magnet of the calledpartys lineswitch to battery. The cut-off relay and relay H ener gize inseries in this circuit and the latter at armature 229 completes alocking circuit for itself over its upper winding. Relay H moreover atarmatures 225 and 232 connects up wipers 233 and 234, at armature 226closes a circuit for giving ringing tone to the calling party, atarmature 227 prepares a circuit for the supervisory lamp, at armature228 applies direct earth to test wiper 235 and opens the circuit ofrelay E, at armature 230 connects earth to the lower winding of the backbridge relay D and at armature 231 opens the impulsing circuit toprevent any further operation of the rotary magnet in case thesubscriber should dial again. Re-

lay E is slow to release and when it falls away This slightdelay isdesirable to ensure that ringing current shall not be connected upuntilthe wanted line has been cleared of its normal batter andearthconnections by the operation of t e cut-ofi' relay so that prematuretripping shall not occur. The wanted artys bell is now rung andwhen hereplies y removing his receiver the direct current bridge thus c0111leted across the line serves to operate relay which thereupon atarmature 215 completes a locking circuit over its lower winding inseries with relay E. This latter relay is therefore again operated andat armatures 220 and 224 cuts oil the ringing current and completes thespeaking connection. Back bridge relay D is now operated over the calledpartys loop and at armatures 205 and 206 reverses the connections ofline relay A to conductors 201 and 202 for metering or supervisorypurposes. When the called party replaces his receiver at the end of theconversation, relay D again de-energizes and reverses the current flowover the speaking conductors back to'its original direction and atarmature 204 completes a C11- cuit for the supervisory lamp theprolonged lighting of which indicates that the called party is beingheld because the calling party has not hung up. When the calling partyreplaces his receiver, release takes place in the manner previouslydescribed, relay G being operated in parallel with the release magnet toensure that the switch is not marked as selectable until it has properlyrestored to' ment is preferable in some circumstances for.

instance where thereis a possibility of a local call being broken downin favour of a long distance call. Fig. 6 also differs slightly fromFig. 3 as regards the holding circuit of relay H in that the B relaycontact has been included in the circuit of the holding winding insteadof that of the energizing winding.

'T he full operation of the switch will not therefore be traced throughin detail, but it will suffice to point out that relay MD is againoperated when relay B energizes and locks up dependent upon relay D.When thecalled party replies, relay D operates and opens the circuit ofrelay MD whereupon it releases but no metering circuit is completed.When the calling party replaces his receiver, relay A de-energizes andopens the circuit of relay AB which (ls-energizes also after a shortinterval.

Relay AB opens the circuit of relay B but since relay B is slow torelease there is a short time durin which relay AB is (lo-energized andrelay energized. Relay H it will be noted is dependent upon relay B.Accordingly a circuit is now completed from earth, back contact andarmature 251, back contact and armature 252, armature 253 and its frontcontact to the metering lead 254. This circuit is maintained untilarmature 253' restores on the de-energization of relay H following therelease of relay B. Relay C is en- I ergized during the releaseoperation as before and applies earth to the test conductor for guard ngpurposes. 'It will be noted that in case no reply is obtained or if thecall isextended to an operator, relay MD will be maintained energizedand accordingly will not commence. to release until relay B has fallenaway at which time the circuit of relay H will be opened so that themetering circuit cannot be completed. a

Fig. 7 is similar to Fig. 6 except that metering is effected by theconnection of booster battery to the test conductor instead of by earthpotential to aseparatemeteringlead and that the H relay contacts'in themetering circuit are unnecessary as the test conductor extends overcontacts of relay B. The operation, however is substantially similar,booster battery being connected up during the time that relay B isfalling away. Moreover as in the previous 'case if the call isunsuccessful or has been extended to an operator, relay MD will notcommence to release until relay B is de-energized and thus it will notbe possible for the metering circuit to be completed.

The arrangement shown in Fi s. 6 and 7 whereby the locking winding 0relay H, which extends to battery, is connected to the test lead overcontacts of relay B overcomes a possible disadvantage in that if thiswinding is connected direcfi, then when the holding earth is removed toe ect release, the battery which is applied until relay H falls away issimilar except as regards itsresistance to the idle potential and mighttherefore in particularly unfavorable circumstances cause aultyoperation. In view, however, of the extremely short release time ofrelay H this possibility is extremely remote. The difficulty such as itis can also be overcome b arranging that in Fig. 1 for instance, theront contact of armature 5 is connected directly to earth instead of thetest conductor 3, thereby producing successive release of a train ofswitches in a forward direction.

said switch responsive to said seizure for disconnecting said one poleof battery from said conductor and for connecting the opposite pole ofbattery to said conductor to mark said switch busy with a busypotential.

necting said one pole of battery 'from said conductor and for connectingthe opposite pole of battery to said conductor to mark said switch busywith a busy potential, means for operating said switchto extend aconnection,

means for connecting the opposite pole of' battery to said conductorover the established connection to maintain said switch in operatedpositionand busy, means for removing said opposite pole of battery fromsaid conductor to release said switch and remove said busy condition,means whereby said switch is unselectable due to the absence of saididle otential during its release, and means whereysaid switch is againselectable responsive to the complete restoration of said switch and theconnection of said idle potential to said conductor.

3. In a telephone system, an automatic hunting switch having an incomingtest conductor, means in said switch for normally connecting one pole ofbattery to said test conductor to apply an idle potential, means forseizing said switch if idle, means in said switch responsive to. saidseizure for discomnecting said one pole of battery from said conductorand for connecting the opposite pole of battery to said conductor tomark said switch busy with a busy potential, a test wiper for saidswitch, means for operating said switch and wiper to extend aconnection, means for disconnecting said opposite pole of battery fromsaid conductor responsive to the establishment of said connection, andmeans for connecting the opposite pole of battery to said conductor byway of said test wiper to maintain said switch busy and in operatedposition.

4. In a telephone system, an automatic switch having line wipers and'atest wiper, trunk lines each having line contacts and test contactsaccessible to said line and test wipers, means for operating said wipersover said contacts to hunt for an idle one of said trunk lines, a relayin said switch for connecting the talking conductors of said switch withsaid line wipers, means. in said switch for connecting one terminal ofthe winding of said relay to said test wiper during the huntingoperation, and means in said switch for connecting a source of potentialto the other terminal of said winding each time the test wiper engages adifferent test contact.

5. In a connector switch for completing connections to called lines,means for selecting and operating said switch to extend a connection toone of said lines, a busy relay operated 1n case said switch extends-aconnection to a busy bus to indicate the busy condition thereoff meansfor releasing said switch,

means or a ain operatin said rela dur' the release t said SWltCl I, andmezns cb ii trolled by the operation of said ,relay for making saidswitch-unselectable until the switch is fully restored to its normalposition. 6. In a telephone system, a calling line, an automatic switch,means responsive to a call by the calling line for seizin said switch,"a first relay in said switch aving two circuits, a slow relay in saidswitch energized responsive to-the seizure of said switch for energizingsaid firstrelay over the first of said circuits means controlled by theenergization of sai first relay'for marking said switch busy, anoperators position,

means for operating said switch to exten the connection from the callingline to said operators position, means responsive to the callingsubscriber replacing his receiver for deenergizing said slow relay, anda third relay in said switch energized res onsive to the deenergizationof said slow re ay for maintaining said first relay energized over thesecond of said circuits in order to maintain said switch busy.

7. A telephone system as claimed in claim 1 in which off-normal contactsin said switch are included in the means for normally conmally connectedto said idle potential, a test wiper in said switch having access tosaid test contacts, means for operating said switch and test wiper toconnect with one of said trunk lines, and means in said switch forapplying the opposite pole of battery to the test contact of theconnected trunk line over said test wiper to mark such trunk line busy.

9. In a telephone system as claimed in claim 1 including a test wiper insaid switch, a driving magnet in said switch for operating said wiper inits hunting movement, and a circuit for operating said driving magnetcompleted independently of said test wiper as long as said test wiperencounters busy potentials during the hunting operation.

10. In a telephone system as claimed in claim 1 including line wipersand a test wiper for said switch, a relay in said switch for connectingthe talking conductors of said switch to said line wipers, and a circuitfor energizing said relay including said test wlper.

11. In a telephone system as claimed in claim 1 including two relays insaid switch, means for energizing the first of said relays forconnecting the opposite pole of battery to potential is inuse theretoonly as long as sald SW1 means for'deenergizing said first relay and forreleasing said switch, and means for energizing the second of saidrelays to aplply said uarding potential to said conductor uring t erelease of said switch.

12. In a telephone system as claimed in claim '1 including two relays insaid switch,

means for energizing the first ofsaid relays forconnectlng the oppositepole of battery to said conductor to apply a guardlng potential theretoonly as long as said switch is in use, means for deenergizing said firstrelay, means responsive thereto for releasing said switch and forenergizing the second relay, means controlled by the energization ofsaid second relay for applyin said guarding potential to said conductoruring the release of said switch, and means whereby the energization ofeither of said relays disconnects said idle potential from saidconductor.

13. In a telephone system as claimed in claim 3 in which when release isinitiated the opposite pole of battery extending by way of said testwiper is removed, means for re leasing said switch and precedingswitches responsive thereto, and means whereby when said switch is fullyrestored said idle potential is connected to said test conductor torender said switch available for use in other connections.

14. In a telephone system as claimed in claim 4 including a magnet fordriving the switch in its hunting operation and a second relay forconnecting said source to said other terminal of said winding each timethe test wiper engages a different test contact, an energizing circuitfor said second relay, and means controlled by said magnet forintermittently closing said circuit on each operation of said magnet.

15. In a telephone system as claimed in claim 4 including a magnet fordriving the switch in its hunting operation and a second relay forconnectin said source to said other terminal of said wlnding each timethe test wiper engages a different test contact, an energizing circuitfor said second relay, means controlled by said magnet forintermittently closing said circuit on each operation of said magnet, anenergizing circuit for said magnet, and means controlled b eachenergization of said second relay for opening said ma net circuit.

' 16. In a telep one systeni as claimed in claim 4 including a magnetfor driving the switch in its hunting operation and a second relay forconnecting said source to said other terminal of said winding each timethe test wiper engages a different test contact,

an energizing circuit for said second relay, means controlled by saidmagnet for intermittently closing said circuit on each operaenergizationof said secondrela for opening said magnet circuit, a set 0 springs insaid switch, means for operatin said springs in case said wipers areoperate beyond said contacts when all said trunk. lines are busy, and alocking circuit for said second relay completed responsive to theoperation of said springs for preventing further operation of saidwipers.

17. In a tele hone system as claimed in claims 4, inclu ing a testconductor in said switch, means for energizing said relay over a circuitincluding said test wiper, said winding, and said source of potential,and a locking circuit including said test conductor completed for saidrelay responsive to its energization.

18. In a telephone system as claimed in claim 4 including a drivingmagnet in said switch for controllin the hunting operation, a drivingcircuit for operatmg said magnet, means for energizing said relay over acircuit including said test wiper, said .ergized responsive to theseizure of said switch for energizing the'said first relay over thefirst of said circuits, means controlled by the energization of saidfirst relay for marking said switch busy automatic switches, anautomatic subscriber s line, means responsive to a call by the callingsubscriber for o crating said switch and automatic switc es to completea connection to said automatic subscribers line, a third relay in saidswitch, a loop circuit including both talking con- .ductors of saidswitch for energizing said third relay when a connection is extended tosaid automatic subscribers line over said automatic switches, anoperators position, means for operating said" switch to extend theconnection from the calling line to said operators position, meansresponsive to the calling subscriber replacing his receiver fordeenergizing said slow rela a circuit including only one of the spea 'ngconductors of said switch for energizlng said third relay, and meanscontrolled by the energization of said third relay for maintaining saidfirst relay energized over the second of said-circuits in order tomaintain said switch busy.

20. In a telephone system as claimed in claim 6 wherein the energizationof said third relay and the maintained energization of said first relayprevents the release of said switch by the calling subscriber.

21. In a telephone system as claimed in claim 1 including means foroperating said switch in a primary directive movement, a relay in saidswitch energized durin the rimary movement and deenergized t erea er toinitiate the secondary movement of said switch, means for releasing saidswitch, and means responsive thereto for energizin said relay to connectsaid 0 posite pole o battery to said conductor uring the release of saidswitch. v

In testimony whereof we have signed our names at Liverpool, England,this 20th day of July, 1929.

WILLIAM HENRY PAULETT. CHARLES GILLINGS.

